With development of large-scale integrated circuits, intensity and running speeds of components in the circuits increase rapidly, and a conventional manner of communication based on electrical interconnection encounters a bottleneck. This is because a connection size for electrical interconnection is very small, and consequently, an electrical interconnection delay is greater than a running speed of a component, and normal running of the component is affected. In addition, high component wiring intensity also brings a serious parasitic effect, severe crosstalk, and high power consumption.
Due to the foregoing deficiencies of electrical interconnection, optical interconnection with its advantages such as a low delay, high electromagnetic compatibility, low power consumption, and high bandwidth, has become a key technology for overcoming the deficiencies of electrical interconnection. As shown in FIG. 1, FIG. 1 is a schematic diagram of typical optical signal transmission based on an optical interconnection technology. It can be seen from FIG. 1 that, for the purpose of transmitting an electrical signal from a component A to a component B, the electrical signal is loaded to an optical wave by means of modulation to form an optical signal, then the formed optical signal is transmitted over an optical fiber, then a detector receives the optical signal and performs operations such as signal conversion and demodulation, and finally the source electrical signal is obtained and transmitted to the component B to complete the entire transmission process.
In the optical signal transmission process shown in FIG. 1, a very important part is a light source used to load the electrical signal. A light source that is used currently is laser light emitted by a laser. A generally used laser includes an edge-emitting laser (for example, a distributed feedback (DFB) laser) and a surface-emitting laser (for example, a vertical-cavity surface-emitting laser (VCSEL)). Compared with the edge-emitting laser, the surface-emitting laser has considerable application scenarios thanks to the following advantages. (1) The surface-emitting laser can be directly modulated, has high modulation efficiency, and requires a low threshold current; (2) temperature drift is slight, and thermoelectric cooling is not required; and (3) an electro-optical conversion rate is high and power consumption is low.
In the optical signal transmission process shown in FIG. 1, light emitted from a laser needs to be coupled into a core of the optical fiber. For example, when the laser that is being used is a VCSEL, and the optical fiber that is being used is a single-mode optical fiber, light emitted from the VCSEL needs to be coupled into a core of the single-mode optical fiber. However, a mode field diameter (MFD), namely a diameter corresponding to a maximum area occupied by a transverse-mode mode field of the optical signal) of the light emitted from the VCSEL is tens to a hundred micrometers (μm) (for example, 50 μm to 100 μm) while a core diameter of the optical fiber is 6 μm to 10 μm. In this case, as shown in FIG. 2, a severe mode field diameter mismatch exists between the VCSEL and the single-mode optical fiber, resulting in a low rate of coupling the light emitted from the VCSEL and the single-mode optical fiber.
In addition to existing between the VCSEL and the single-mode optical fiber, the mode field mismatch problem (including that a mode field diameter of light emitted from a laser is far greater than a core diameter of an optical fiber, or is far less than a core diameter of an optical fiber) may also exist between a laser of another type and a single-mode optical fiber (or a multi-mode optical fiber). Therefore, a proper manner is required to shape an optical signal emitted from the laser, so that a spot diameter of the adjusted optical signal matches a core diameter of an optical fiber, and the optical signal can be coupled into the optical fiber in high efficiency.